Turning multiple materials into one texture
Baking is the way to go. If you're in blender internal, baking is very straightforward. If using Cycles it is a little more complex but can give great results. Create an image for each map that you need, open that image and select the node in the Cycles node editor, then bake the map you need in the bake panel. It can combine the diffuse map from multiple UV projections, procedural materials etc.